Electrospun Poly(vinylidene fluoride) Nanocomposites with Ionic Liquid Functionalized Graphene Nanoplatelets by a Noncovalent Method for Piezoresistive Pressure Sensor Applications

Piezoresistive pressure sensors have been prepared by the electrospinning of poly(vinylidene fluoride) (PVDF) containing graphene nanoplatelets (GNP) functionalized using 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM(OTf)) ionic liquid (IL). Optical microscopy demonstrated that the functionalized GNP powder presented particles with a smaller lateral size. The obtained mats were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, electrical resistivity using two and four probes, and electromechanical testing with up to 32 load–unload cycles. Functionalization with BMIM(OTf) resulted in a higher PVDF electroactive phase. Electrospun mats obtained without the IL displayed a signal comparable to noise, while mats obtained with the BMIM(OTf) functionalized GNP displayed a clear signal, indicating that the IL helped with the dispersion of GNP on the PVDF matrix. Electrospun mats containing 1.0%m functionalized GNP presented the best performance among the evaluated samples, presenting low hysteresis and a lower distribution of the read values especially in the working range of 0 to 250 kPa. The piezoresistive behavior of the sample was tested under 32 load–unload cycles, remaining stable. Higher ranges of axial load resulted in the rupture of the fibers and swift degradation of the piezoresistive signal under a high number of cycles. A simple load cell was assembled to demonstrate the capacity of the membranes to act as piezoresistive compressive sensors capable of detecting the pressing of a human finger and differentiating between applied weights.